Redditors captured national headlines last month by driving the price of GameStop stock over 14,000%, catching bearish institutional investors in a classic “short squeeze.” A spike last Wednesday drove the shares up 40% and sent the broader market into a frenzy. Everyone wanted in on the action. New “meme stocks” like AMC, Nokia, and Blackberry—hot brand names from 2005—percolated up from the online ferment to ride the tail winds of GameStop’s success. Dave Portnoy of Barstool Sports purportedly invested a million bucks in a handful of these names. Others followed. I followed. On Wednesday, 1.25 billion shares of AMC were...